This invention is concerned with an oil base packer fluid for hydrocarbonaceous fluid wells such as oil and gas wells and a method for completing such wells, particularly wells drilled through the permafrost zones of the earth.
In many frigid areas of the world such as Northern Alaska and Canada, oil and gas wells are drilled through permafrost which is a permanently frozen layer at variable depth below the earth's surface. This permafrost presents a great obstacle to the removal of relatively warm fluids through the well pipe. The warm fluid in the well pipe causes thawing of the permafrost in the vicinity of the well. This thawing in turn causes disintegration of the well wall and subsidence of the surface. The warm gas or oil coming to the surface in the well pipe becomes cooled in giving up its heat to the permafrost and forms hydrate crystals which may freeze together and block the well pipe.
One method to alleviate this blockage problem is to place a gelatinous oil-based packer fluid as a thermal insulator in the annular space between the well pipe and well wall. Such insulating fluid is usually an oil to which has been added gel-building concentrates and a catalyst. At this fluid is pumped down the well hole in the annular space, gelatin of the fluid occurs depending on time and shear developed on the fluid. The so-gelled packer fluid decreases the heat transfer between the warm gas or oil rising in the well pipe and the well wall.
Although this method is effective in theory, it has been difficult to control gelation of the fluid. Thus, one problem associated with this method is that of gelation of the fluid before it is completely placed in the well due to mechanical problems, particularly pump failure. This premature increase in viscosity decreases the pump efficiency and increases the placement time and power requirements for placement. Expense is another important factor in designing a packer fluid for permafrost use.
In U.S. Pat. No. 3,618,680 to J. D. Ellard, a drilling fluid is provided consisting essentially of oil containing a minor but effective viscosifying amount, not exceeding 4.5 pounds per barrel, of at least one of subdivided asbestos and subdivided silica and containing substantially no water. Generally, the drilling fluid is cooled to below 27.degree. F., but not below about 0.degree. F. before use.
In U.S. Pat. No. 3,700,050 to L. H. Miles, a packer fluid is provided comprising a hydrocarbonaceous oil base fluid having a freezing point below 14.degree. F. and having incorporated therein a thermal insulating and/or weighting amount of hollow shapes of glass or plastic and, optionally, halogenated ethane and/or halogenated ethylene. Although the packer fluid may perform satisfactorily, the high cost of the components and high transportation costs associated with the low bulk density hollow shapes render it economically prohibitive.
In U.S. Pat. No. 3,719,601 a liquid insulating medium is provided for use in insulating thermal injection wells, wells drilled through permafrost, and pipelines traversing a permafrost region. The medium comprises a mineral oil containing from 1% to 10% by weight of a fibrous finely-divided magnesium silicate or asbestos. Such insulating medium is very expensive due to the cost of the highly refined mineral oil used and, depending on the concentration of magnesium silicate or asbestos, has a high viscosity which makes placement of the medium within an annular space difficult.
In U.S. Pat. No. 3,831,678, an oil base packer fluid is described containing an organophilic clay gellant which will not yield or form a thick grease-consistency oil at temperatures below 50.degree. F. This fluid can be easily pumped into the annulus opposite the permafrost as long as the temperature of the fluid does not exceed about 50.degree. F. As such, this method is limited to ambient temperatures below 50.degree. F. where the oil base packer fluid will not thicken during preparation prior to placement downhole.
Other methods of alleviating problems associated with the production of oil and gas in wells drilled through permafrost are described in the following references and U.S. Patents: WORLD OIL, p. 85 (January 1970); PETROLEUM ENGINEER, pp. 39-41 (February 1972); THE OIL AND GAS JOURNAL, p. 56 (January 24, 1972); U.S. Pat. Nos. 3,642,065; 3,662,832; 3,677,340; 3,685,583; and 3,695,351.
The present invention provides a relatively inexpensive oil base packer fluid containing an organophilic clay gellant and certain polyfunctional amino silanes. This fluid is thin and pumpable when prepared at temperatures less than about 130.degree. F. but will gel to a thick grease consistency after placement downhole in an oil or gas well at temperatures above about 130.degree. F. The so-gelled oil base packer fluid is an excellent insulator preventing the high temperatures within the well bore from thawing the permafrost. The oil base packer fluid is also useful in regular oil and gas wells, and in steam injection wells.
The fluid can be prepared at relatively high temperatures as for example in warmer weather without concern as to premature thickening before placement downhole.